The invention relates to a multi-station communication bus system having at least one master station and at least one slave station, any master station comprising arbitration means per frame for transmitting an arbitration signal, and for detecting a negative or positive arbitration result, depending an arbitration signal of any other station. The master station also comprises transmission means for transmitting a message after a positive arbitration result. The frame comprises a slave station address with a slave control signal, followed by a series of data byte spaces up to a predetermined maximum number per frame, each time with signalling of a "last/non-last" data byte of said message and space for the directly subsequent communication of a data byte acknowledge signal. A system of this kind is known from Netherlands Patent Application 8002345 and the corresponding U.S. Pat. Specification No. 4,429,384 (PHN 9737). The reference relates to a single-channel system; however, the invention is just as useful in a more extensive system, for example with a separate clock wire. The bus may be galvanic; it can alternatively be realized by optical means. The arbitration means are effective in that the bus realizes a wired logic function, for example a wired AND-function. This can be done by means of an open collector connection of the stations and the like: each station supplying a logic O then masks any logic 1 delivered by any other station. The operation is the same in the case of an optical system.
The known system is well-defined at the bit level, but does not describe the actions to be undertaken when one of two communicating stations is incapable of correctly processing the information applied to it in case of multi-byte messages.